5-methoxypsoralen (5-MOP) caused less nausea than 8-methoxypsoralen 8-MOP) so as 5-MOP is unavailable now we need to consider approaches to this adverse effect. (We are still hoping an NHS orphan drug manufacturer might be able to start producing 5-MOP.)
Nausea is common with 8-MOP, affecting about a quarter of patients but can if necessary be coped with by some (because we had the option of 5-MOP it was used for some who were affected but not severely) but for others is difficult to manage, for example causing patients to have to get off the bus when coming in for the UVA part of PUVA in order to vomit.
- When a patient who has had previous PUVA (and who was on 5-MOP, usually because of nausea with 8-MOP) is referred it is worth exploring how bad was the nausea (could the patient “put up” with it). Taking the medication with a small snack (not too much food as there is a lot of first pass metabolism so slowing absorption with a large meal allows the liver enzymes to inactivate even more before it gets into the circulation and hence the skin) can help.
- If this is likely to be inadequate an anti-emetic, e.g. ondansetron* 8mg two hours before psoralens are taken, is appropriate. Alternative antiemetics include metoclopramide 10mg and cyclizine 50mg. There is no evidence as to which antiemetic is most effective for psoralen nausea (which is probably mainly due to actions on the brain rather than the gut), so choice is an individual prescriber decision.
*An appropriate first-line anti-emetic for adults, although not ideal if early pregnancy is possible (we do not use PUVA if likely) or if QT interval possibly prolonged (e.g. by high dose antihistamines).
- Of the two microcrystalline tablet forms of 8-MOP “Meladinine” 8-MOP, as well as being just as effective and cheaper, produces less nausea than “PUVA psoralen” 8-MOP and is to be used if possible (there may be supply issues).
- 8-MOP bath PUVA and 8-MOP soaks, for the indications in which they can work, usually avoid nausea as the amount absorbed through the skin is lower than when given by mouth. However, these treatments are more time-consuming for patients and staff than oral PUVA and involve patients spending longer times in hospital (which we are particularly trying to reduce now because of COVID-19). Furthermore, in many indications oral PUVA is preferable to PUVA bath and soaks (see PUVA guidelines).
Adapted from Dr Robert Dawe 18.9.2021 Photobiology Unit, Ninewells Hospital